Particle swarm optimization assisted multiuser detector for M-QAM DS/CDMA systems

This paper analyzes the particle swarm optimization multiuser detector (PSO-MUD) under high-order modulation schemes, (particularly for M-QAM), in DS/CDMA systems single-input-single-output (SISO) multipath channels. In order to avoid the computation of complex-valued variables in high-order squared modulation, the optimization problem is reformulated as a real-valued problem. Considering previous results on literature for low-order modulation formats (usually binary/quadrature phase shift keying - BPSK/QPSK), a performancetimescomplexity trade-off comparison is carried out between PSO-MUD and local search multiuser detector (LS-MUD). Performance is evaluated by the symbol error rate (SER), and complexity by necessary number of cost function calculations for convergence. If the background for BPSK heuristic multiuser detection (HEURMUD) problem indicates that the 1-opt local search method is enough to achieve excellent performancetimescomplexity trade-offs, our Monte-Carlo simulation results and analysis show herein indicate the LS-MUD presents a lack of search diversity under high-order modulation formats, while the PSO-MUD is efficient to solve the MUD problem for high-order modulation schemes.